This invention relates to a filter arrangement in general and more particularly to a filter arrangement with an improved flow path.
Tubular filter bodies with at least one tubular filter structure with a porous wall, through which a liquid passes substantially radially, particles above a given size being held back at the entrance surface, made of porous plastic, ceramic material, metal, graphite, etc. are known. They serve either directly as filter bodies or as supports for a filter diaphragm which has been formed from a liquid phase at the entrance surface of the filter body and permits particularly fine filtration. With diaphragm filtration, mixtures of solvents and dissolved particles can be separated. The separated particles are held back at the surface of the diaphragm.
If the solvent and the dissolved component of the solution to be filtered have approximately the same molecular dimensions, such as is the case, for instance, with rock salt and water, the separating process is called inverse osmosis. As the separating process proceeds against the osmotic pressure, the pressure on the solvent side must exceed the osmotic pressure if filtration is to come about. The necessary pressures can be substantial; a 10% rock salt solution, for instance, has an osmotic pressure of 80 atm, which must be overcome.
If the molecular dimensions differ substantially from each other, one speaks of ultrafiltration. Ultrafiltration finds application for concentrating, fractionating or purifying macromolecular solutions. Because the molecular weight of the dissolved component is high as compared to the solvent, generally higher than 2000, the solutions have only low osmotic pressure, and the separation can be carried out in these cases at relatively low pressures, for instance, at 1 to 10 atm.
The particles to be separated are held back at the surface of the diaphragm. Unless they are transported away by suitable measures, i.e., if, for instance, the liquid to be filtered is substantially stagnant in front of the entrance surface, there is formed in the course of the operation a layer of the separated particles which lowers the permeability of the filter arrangement or increases the pressure that must be supplied. Such a filter arrangement must therfore be cleaned of the layer formed at regular intervals.